Structured Latex Particles Research Articles

Correction: Designed incorporation of semi-crystalline domains into structured latex particles via solvent-aided emulsion polymerization

Correction for ‘Designed incorporation of semi-crystalline domains into structured latex particles via solvent-aided emulsion polymerization’ by Adrián Perez et al., Polym. Chem., 2022, 13, 5636–5646, https://doi.org/10.1039/D2PY00926A.

Designed incorporation of semi-crystalline domains into structured latex particles via solvent-aided emulsion polymerization

We describe an emulsion polymerization route towards the design of structured latex particles containing semi-crystalline domains with improved mechanical properties.

Structural interaction of semi-interpenetrating polymer network polyurethane/styrene acrylonitrile latex particles

A series of novel structured latex particles with semi-interpenetrating polymer network (IPN) of glassy styrene-acrylonitrile copolymer (SAN) cores and rubbery polyurethane (PU) shells were synthesized to improve damping property. The inverted core/shell synthesis method (rubbery part first, then the glassy part) was applied to control morphology of core/shell latex particles. The glass transition temperature and mechanical property of the obtained semi-IPN were characterized by DMA and UTM, respectively. The effect of composition on the mechanical properties of core/shell latex IPN particles was studied. It was found that the core/shell latex particles with high crosslinking density are more miscible than those with low crosslinking density. Additionally, the improved tensile strength and elongation were observed. Therefore, the crosslinking efficiency of PU plays an important role in governing phase miscibility in core/shell latex IPN particles.

Design and fabrication of PVAc-based inverted core/shell (ICS) structured adhesives for improved water-resistant wood bonding performance: I. Influence of chemical grafting

Strategy for fabricating inverted core/shell (ICS) structured latex particles to improve the water- and heat-resistance of PVAc-based adhesives was investigated. A grafting layer was fabricated with acrylonitrile (AN) to achieve a thermodynamic non-equilibrium ICS morphology with a hydrophilic poly(vinyl acetate) (PVAc) core and a hydrophobic polystyrene (PS) shell. The function of the grafting layer was explored by tuning the AN loading levels and core-to-shell ratios. Special latex particle morphologies, transferring from strawberry-like with secondary PS particles, over neat strawberry-like, to final ball-like morphology, were observed and verified by electron microcopies. The wood adhesive performance of PVAc-based latex adhesives, particularly for heat- and water-resistant bonding, were evaluated by shear strength at both dry and wet conditions, as well as the boiling water failure time, showing a significant enhancement of boiling water resistance. This general approach opens an avenue for controlled design and manufacture of high-performance emulsion-based adhesives containing structured particles.

Polymerization Induced Phase Separation in Composite Latex Particles during Seeded Emulsion Polymerization

Multiphase structured latex particles have been studied and produced for decades; however, the mechanism governing the polymerization induced phase separation process in such particles remains incomplete. These particles are typically produced by starting with a first, single phase polymer particle dispersion, and then a second polymer, nearly always thermodynamically phase incompatible with the first, is polymerized within those seed particles. The Gibbs free energy change upon demixing is the driving force inducing polymer–polymer phase separation during polymerization (PIPS). However, the ultimate extent of phase separation is dictated by resistances to mutual polymer chain diffusion within the latex particles. Here, we have elucidated and quantified the contributions of thermodynamic driving force and kinetic diffusive limitations to polymer–polymer phase separation within composite nanoparticles. We present a means to evaluate both the influence of chemistry and process conditions on a master plot pr...

Three-layer structured soft particles to construct photonic paper exhibiting responsive spatio-temporal color patterns

Photonic crystals (PCs), which generate vivid colors from periodic physical structures, have attracted considerable attention. However, it is still highly challenging to produce large-scale PC films with high mechanical performance. To address the challenge, a new strategy to fabricate PC films from soft structured latex particles instead of widely used hard particles is reported. The soft latex particles are designed to have a three-layer structure: a responsive poly(acrylic acid) (PAA) corona, hard polystyrene (PSt) shell and soft poly(n-butyl acrylate) (PnBA) core. Such latex particles with easily-tunable and well-defined structures are synthesized from RAFT emulsion polymerization. Thanks to the softness, PCs can be easily achieved by latex casting on various substrates without pre-treatment, leading to a dense, crack-free, and mechanically robust PC film. The as-prepared PC films of the particles with PnBA around 55 wt% can generate vivid colors when the “inks” of water and hydrophilic liquids are applied. The full colors can be achieved by tuning particle size or pH value. Taking advantage of the responsive properties to hydrophilic liquids with different volatilities, both temporary and permanent patterns can be constructed on the PC films, leading to spatio-temporal colorful patterns. The method is simple, scalable-up, and versatile, showing great potentials for practical applications.

Effect of Shell Growth on the Morphology of Polyvinyl Acetate/Polystyrene Inverted Core-Shell Latex Fabricated by Acrylonitrile Grafting.

A novel strategy for fabricating inverted core-shell structured latex particles was implemented to investigate the morphology and properties of polyvinyl acetate (PVAc)-based latex. In this study, active grafting points were synthesized onto the surface of PVAc latex cores via grafting acrylonitrile (AN) to obtain a controllable coating growth of the shell monomer, styrene (St). The effect of shell growth on the morphological evolvement was explored by tuning the time of shell monomer polymerization. Unique particle morphologies, transferring from “hawthorn” type, over “peeled pomegranate” type, to final “strawberry-like” type, were observed and verified by electron microscopy. The morphological structure of latex particles exerted a significant effect on the particle size, phase structure, and mechanical properties of the obtained emulsions. The water-resistance of PVAc-based latex was also evaluated by the water absorption of latex films. More importantly, the experimental results provided a reasonable support for the controlled growth of St monomer, that is, the self-nucleation of dispersive St monomer can be transformed to in-situ coating growth on the PVAc core surface depending on the AN-active grafting points. This fabricating approach provides a reference for dynamical design and control of the latex particle morphology.

Rational design and synthesis of transition layer-mediated structured latex particles with poly(vinyl acetate) cores and poly(styrene) shells

The synthesis of structured latex particles containing hydrophilic poly(vinyl acetate) (PVAc) cores and hydrophobic poly(styrene) (PS) shells mediated by a controllable transition layer was reported. A transition layer was fabricated onto PVAc cores by introducing a coupling monomer and butyl acrylate (BA), prior to polymerization of second-stage St-based monomer mixture. While such structured PVAc/PS latex particle obtained was thermodynamic non-equilibrium, straightforward synthetic route of the transition layer can be optimized so that the particle morphology is kinetically achievable. Analysis by transmission electron microscopy shows that the particle morphology is highly influenced by both the transition layer composition and PS-based polymer composition. Two-phase particle morphology without transition layer was an inverted acorn-like structure with single PS core wrapped by PVAc shells. The particle morphology mediated by transition layer varied from that of a broken egg shell-like structure with PS-based coating, over intermediate structures in which uniform PS protuberances surrounded PVAc cores, to core/shell structure with single PVAc core. This general approach may offer a number of possibilities for design and synthesis of kinetically controllable phase-separation morphologies for a variety of applications.

Effect of molar mass on film-forming properties of self-crosslinking latexes based on structured acrylic microgels

Abstract The influence of molar mass of the shell layer of latex particles having core–shell morphology on film-forming and final coating properties of self-crosslinking latexes based on keto-hydrazide crosslinking system was investigated. Structured latex particles were prepared by the semi-continuous non-seeded emulsion polymerization of acrylic monomers. The particle core was slightly crosslinked to prevent the copolymers forming the core phase from migration into the shell phase. The molar mass of copolymers forming the shell phase was gradually reduced by isooctyl 3-mercaptopropionate chain transfer agent included in the synthesis of the shell layers. The results confirmed theoretical predictions and revealed that even a slight amount of chain transfer agent added during the synthesis achieved a substantial lowering of minimum film-forming temperature and reduction of water sensitivity of latex coatings.

Preparation and Property Study of Core-Shell Ambient-Temperature Crosslinkable Polyacrylate Binder

As the binder of waterborne inks, the capability of acrylic polymer has great influences on the quality of inks. In this contribution, structured latex particles with a poly (stryrene-butyl acrylate-methacrylate) core and a poly (butyl acrylate-methyl methacrylate-methacrylic acid-diacetone acrylamide (DAAM)) shell, which can be used as binders of water-based ink, were prepared by emulsion polymerization. The emulsion can cure in the course of film forming at ambient temperature through the reaction between DAAM and the adipic acid dihydrazide (ADH). Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), transmission electron microscopy (TEM), atomic force microscopy (AFM) were used to characterize the structures and study the properties of the latices. The drying time of the crosslinking latices was investigated. In addition, influences of DAAM monomer dosage and the mole ratio of DAAM to ADH on the mechanical properties of self-crosslinkable core-shell latices were also discussed. It was found that the core-shell crosslinkable particles with a low glass transition temperature (Tg) core and a high Tg shell have better film properties and would be more applicable to binders of water-based ink for plastic film, in comparison with those particles with a high Tg core and a low Tg shell.

Monte Carlo Simulation of Emulsion Polymerization Kinetics and the Evolution of Latex Particle Morphology and Polymer Chain Architecture

AbstractMonte Carlo methods were applied to the reaction kinetics and polymer diffusion at play during the dynamics of creating structured latex particles. Reaction kinetic events in both the water phase and the particles are combined with diffusion of polymer radicals in the particles to allow the prediction of the overall polymerization kinetics, including the Trommsdorf gel effect, chain transfer reactions to monomer, chain transfer agents (e.g., thiols) and polymer chains, and chain length dependent termination reactions. This allowed the calculation of latex particle morphology, as well as the polymer molecular weight, gel content and graft level, when applicable. A number of examples are used to provide experimental data with which to compare the Monte Carlo predictions.magnified image

Preparation and properties of core [poly(styrene‐n‐butyl acrylate)]–shell [poly(styrene–methyl methacrylate–vinyl triethoxide silane)] structured latex particles with self‐crosslinking characteristics

AbstractStructured latex particles with a slightly crosslinked poly(styrene‐n‐butyl acrylate) (PSB) core and a poly(styrene–methacrylate–vinyl triethoxide silane) (PSMV) shell were prepared by seed emulsion polymerization, and the latex particle structures were investigated with Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, transmission electron microscopy, and dynamic light scattering. The films that were formed from the structured core (PSB)–shell (PSMV) particles under ambient conditions had good water repellency and good tensile strength in comparison with films from structured core (PSB)–shell [poly(styrene–methyl methyacrylate)] latex particles; this was attributed to the self‐crosslinking of CH2CHSi(OCH2CH3)3 in the outer shell structure. The relationship between the particle structure and the film properties was also investigated in this work. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1824–1830, 2006

Dynamics of shear-thinning suspensions of core–shell structured latex particles

The rheological behavior and microstructure of shear-thinning suspensions of core–shell structured carboxylated latex particles were examined. The steady shear viscosity of the suspension increased with increasing dissociation of the carboxyl groups or increasing particle concentration, however the critical shear stress σ c and inter-particle distance ξ of the microstructure did not change. With increasing particle diameter, σ c increased and ξ decreased. These results were consistent with a Brownian hard sphere model, in which competition exists between the bulk mass transfer due to the applied field and diffusion of the particles. We confirmed that σ c depends on ξ, as expressed by σ c = 3 k T / 4 π ξ 3 . This relationship is consistent with the dynamics of a Brownian hard sphere model with particle diameter ξ. Thus the dynamics of shear-thinning suspensions of core–shell particles can be explained by a Brownian thermodynamic model.

The effect of the polymerization route on the amount of interphase in structured latex particles and their corresponding films

Three series of hard/soft styrene–acrylic latex based systems with equivalent compositions were prepared either by blending of homopolymer latexes or by preparing structured latex particles having core shell (CS) or inverted core shell (ICS) morphologies. Transmission electron microscopy (TEM) was used to investigate the particle morphologies, which were correlated to the calculated fractional radical penetration for the propagating species during the reactions. The thermo-mechanical properties as well as the morphology of the resulting latex films were analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and TEM. The viscoelastic properties of the interphase between the first and second-stage polymers formed in the structured hard/soft latex films, as well as its qualitative amount and also the film morphologies were found to depend on the interplay between thermodynamic and kinetic parameters during the synthesis of the samples.

Nonequilibrium particle morphology development in seeded emulsion polymerization. II. Influence of seed polymer Tg

AbstractMost structured latex particles are formed in the nonequilibrium state as a result of the reaction kinetics proceeding faster than the phase separation kinetics. Of the many factors controlling such morphologies, the polarity and glass transition temperature (Tg) of the seed polymer are important. In order to study the direct effect of the seed polymer Tg on morphology, we produced a series of poly(methyl methacrylate)/poly(methyl acrylate) seed copolymers having glass points between 52 and 98°C, and particle sizes between 320 and 390 nm. We then used styrene as a second‐stage monomer reacting in both the batch and semibatch process modes, and utilized reaction temperatures (Tr) between 50 and 70°C. Monomer feed rates were varied between flooded and starve‐fed conditions. The equilibrium morphology for these composite particles is an inverted core–shell structure, but all morphologies obtained in our experiments were nonequilibrium. Under monomer starved conditions only core–shell structures were formed when (Tr−Tg) < 0, but significant penetration of the polystyrene into the acrylic core occurs when (Tr−Tg) > 15°C. These results are reasonably well predicted using the “fractional penetration” model developed earlier. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 905–915, 2003

Effects of surface characteristics on non-specific agglutination in latex immunoagglutination antibody assay

To monitor the non-specific agglutination (NSA) in latex immunoagglutination assay, antigen-coated structured latex particles, which have carboxyl and sulphonate groups as hydrophilic domains, were tested for an antibody assay. Sulphonated particles showed NSA in high antibody concentrations, where no surface antigen left to match with. This was further justified with the more stable highly sulphonated particles, which showed higher degree of NSA. It can therefore be confirmed that sulphonate groups cause (or at least promote) NSA, while carboxyl groups do not. Surface coverage over 17% was not fully utilized for antigen–antibody reaction, due to the prozone effect. The difference in sensitivity of particles was explained in terms of our new explanations on the governing interactions of protein adsorption.

Hydroplasticization effect in structured latex particles film formation

Series of emulsion copolymers with structured particles were synthesized comprising copolymerized acrylic or methacrylic acid in the outer layer. All samples were based on particles, containing identical cores slightly crosslinked by allyl methacrylate and variable shells, weight ratio core/shell being constant 1/1. Each sample contained 10 wt% HEMA in the shell to achieve the film crosslinkability. In both series samples with different hardness and polarity (varible styrene/butyl acrylate ratio) of the shell layer were prepared. It was shown that the extent of particle swelling and hydroplasticization depends not only on the content of dissociated carboxylic groups, but also on the composition and crosslinking of the rest of polymer chain i.e. on its polarity and rigidity and on the origin of carboxylic groups. The effect of dissociated carboxylic groups on lowering the minimum film forming temperature was much more pronounced if the polymer chains were more polar.

Interface and bulk properties in films of phase separated dispersion particles

Structured latex particles are of high interest as tailor made dispersion binders to meet contradictory requirements in different fields of applications. Aqueous dispersions, e.g. used as binders in solvent-free, low pigmented paint formulations, have to cope with the challenge to guarantee an excellent film forming ability at room temperature as well as a low tack. In this work, the synthesis and characterizations of hemisphere-like particles with different chemical constitutions are described. The single particles were placed onto various types of substrates. The particle–surface interface was then investigated by atomic force microscopy (AFM). Characteristic differences were found as a function of the polarity of both, polymer and substrate. Including these findings, AFM was used to determine the impact of the interface structure on the bulk properties of the final dispersion films. The results are compared to computer simulations of the packing of the particulate materials. A correlation of microscopic interface structure to macroscopic application properties of the corresponding dispersion films is presented. The results are compared to sets of blends with identical chemical composition and equivalent volume fraction and the corresponding statistical copolymers.

Morphology, design and characterization of IPN-containing structured latex particles for damping applications

We have prepared a series of novel structured latex particles with interpenetrating polymer network (IPN) cores and glassy SAN shells. The IPN cores were composed of two polymers: polybutadiene-based and acrylic-based. The morphologies of these latex particles were determined by TEM. The glass transition temperature and mechanical behavior of the polymers were characterized by DMS. The effect of different components on the final core/shell particle morphologies and mechanical properties was studied. The mechanical behavior of core/shell particles with IPN cores was also compared with that of separate core/shell and multilayered core/shell particles. In addition, normal core/shell synthesis (rubbery part first, then the glassy part) and inverted core/shell synthesis (glassy part first, then the rubbery part) were performed to provide another access for morphology design and control. It was found that the core/shell latex particles with poly(butyl acrylate)-based copolymers are more miscible than poly(ethylhexyl methacrylate)-based copolymers. The high grafting efficiency of poly(butyl acrylate) plays an important role in governing phase miscibility. The latex particles synthesized by the inverted core/shell mode showed higher miscibility than the normal synthesized ones. The damping properties of different core/shell particles were evaluated based on the loss area (LA) from dynamic mechanical spectroscopy measurements. The IPN core/shell polymers were found to be the best dampers due to their more miscible chemistry. The highest level of damping was achieved by inverting core/shell particles with dual-phase continuity compared to normal core/shell particles.

Structured latex particles with improved mechanical properties

Structured polymer latex particles are prepared by a swelling emulsion polymerization process, in which the initial particles are first swollen by ethylenically unsaturated monomers and the polymerization of the latter is then carried out. This special polymerization process leads to multi-phase particle morphology. Instead of a thermodynamically more favorable large-scale phase-separation, we obtain multiple, near-spherical domains dispersed within the particles. TEM analysis after selective staining reveals the size and distribution of the microdomains. Dynamic mechanical analysis of the polymer films confirms the absence of a distinct, large second phase and indicates that such microdomains interfere at the molecular level with the segmental mobility of the dispersing phase. We present examples of soft polymers as the continuous phase and hard polymers as the dispersed phase. The inclusion of hard microdomains into soft continuous phase increases dramatically both the films tensile strength and elongation, which means improved cohesive strength of the polymer material. The increase in tensile strength of the polymer film correlates directly with the hardness of the dispersed phase. Improvement in tensile strength and elongation is important in a number of industrial applications of polymers, such as flexible coatings, coalescent-free paints and pressure sensitive adhesives (PSAs). Examples are presented which demonstrate the potential applications of the swelling emulsion polymerization process.